Message-ID: <mflwgdnyipdf4reufmbx7qarjcgouct5coe2bllticrabcu6rt@vf3bvmpunimw>
Date: Fri, 6 Feb 2026 17:14:10 +0000
From: Pedro Falcato <pfalcato@...e.de>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, 
	Jarkko Sakkinen <jarkko@...nel.org>, Dave Hansen <dave.hansen@...ux.intel.com>, 
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Subject: Re: [PATCH v2 03/13] mm: add mk_vma_flags() bitmap flag macro helper

On Thu, Jan 22, 2026 at 04:06:12PM +0000, Lorenzo Stoakes wrote:
> This patch introduces the mk_vma_flags() macro helper to allow easy
> manipulation of VMA flags utilising the new bitmap representation
> implemented of VMA flags defined by the vma_flags_t type.
> 
> It is a variadic macro which provides a bitwise-or'd representation of all
> of each individual VMA flag specified.
> 
> Note that, while we maintain VM_xxx flags for backwards compatibility until
> the conversion is complete, we define VMA flags of type vma_flag_t using
> VMA_xxx_BIT to avoid confusing the two.
> 
> This helper macro therefore can be used thusly:
> 
> vma_flags_t flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT);
> 
> We allow for up to 5 flags to specified at a time which should accommodate
> all current kernel uses of combined VMA flags.
>

How do you allow up to 5 flags? I don't see any such limitation in the code?
 
> Testing has demonstrated that the compiler optimises this code such that it
> generates the same assembly utilising this macro as it does if the flags
> were specified manually, for instance:
> 
> vma_flags_t get_flags(void)
> {
> 	return mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT, VMA_EXEC_BIT);
> }
> 
> Generates the same code as:
> 
> vma_flags_t get_flags(void)
> {
> 	vma_flags_t flags;
> 
> 	vma_flags_clear_all(&flags);
> 	vma_flag_set(&flags, VMA_READ_BIT);
> 	vma_flag_set(&flags, VMA_WRITE_BIT);
> 	vma_flag_set(&flags, VMA_EXEC_BIT);
> 
> 	return flags;
> }
> 
> And:
> 
> vma_flags_t get_flags(void)
> {
> 	vma_flags_t flags;
> 	unsigned long *bitmap = ACCESS_PRIVATE(&flags, __vma_flags);
> 
> 	*bitmap = 1UL << (__force int)VMA_READ_BIT;
> 	*bitmap |= 1UL << (__force int)VMA_WRITE_BIT;
> 	*bitmap |= 1UL << (__force int)VMA_EXEC_BIT;
> 
> 	return flags;
> }
> 
> That is:
> 
> get_flags:
>         movl    $7, %eax
>         ret
> 
> Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

Reviewed-by: Pedro Falcato <pfalcato@...e.de>

-- 
Pedro

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